Re: [PATCH] hvf: guard xgetbv call.

[Richard Henderson <richard.henderson@linaro.org>]

On 1/10/21 8:34 AM, Richard Henderson wrote:
> On 1/9/21 3:46 PM, Roman Bolshakov wrote:
>> +static int xgetbv(uint32_t cpuid_ecx, uint32_t idx, uint64_t *xcr)
>>  {
>> -    uint32_t eax, edx;
>> +    uint32_t xcrl, xcrh;
>>
>> -    __asm__ volatile ("xgetbv"
>> -                      : "=a" (eax), "=d" (edx)
>> -                      : "c" (xcr));
>> +    if (cpuid_ecx && CPUID_EXT_OSXSAVE) {
>> +        /* The xgetbv instruction is not available to older versions of
>> +         * the assembler, so we encode the instruction manually.
>> +         */
>> +        asm(".byte 0x0f, 0x01, 0xd0" : "=a" (xcrl), "=d" (xcrh) : "c" (idx));
>>
>> -    return (((uint64_t)edx) << 32) | eax;
>> +        *xcr = (((uint64_t)xcrh) << 32) | xcrl;
>> +        return 0;
>> +    }
>> +
>> +    return 1;
>>  }
> 
> Not to bikeshed too much, but this looks like it should return bool, and true
> on success, not the other way around.

Also, if we're going to put this some place common, forcing the caller to do
the cpuid that feeds this, then we should probably make all of the startup
cpuid stuff common as well.

Note that we'd probably have to use constructor priorities to get that right
for util/bufferiszero.c.


r~